全文获取类型
收费全文 | 20698篇 |
免费 | 1740篇 |
国内免费 | 650篇 |
专业分类
电工技术 | 947篇 |
技术理论 | 1篇 |
综合类 | 1067篇 |
化学工业 | 3968篇 |
金属工艺 | 998篇 |
机械仪表 | 1284篇 |
建筑科学 | 1101篇 |
矿业工程 | 465篇 |
能源动力 | 635篇 |
轻工业 | 1460篇 |
水利工程 | 294篇 |
石油天然气 | 735篇 |
武器工业 | 94篇 |
无线电 | 2760篇 |
一般工业技术 | 3267篇 |
冶金工业 | 1138篇 |
原子能技术 | 254篇 |
自动化技术 | 2620篇 |
出版年
2024年 | 71篇 |
2023年 | 338篇 |
2022年 | 489篇 |
2021年 | 724篇 |
2020年 | 595篇 |
2019年 | 494篇 |
2018年 | 635篇 |
2017年 | 663篇 |
2016年 | 629篇 |
2015年 | 737篇 |
2014年 | 1007篇 |
2013年 | 1309篇 |
2012年 | 1234篇 |
2011年 | 1316篇 |
2010年 | 1168篇 |
2009年 | 1105篇 |
2008年 | 1049篇 |
2007年 | 1044篇 |
2006年 | 1064篇 |
2005年 | 844篇 |
2004年 | 651篇 |
2003年 | 694篇 |
2002年 | 781篇 |
2001年 | 636篇 |
2000年 | 494篇 |
1999年 | 512篇 |
1998年 | 522篇 |
1997年 | 422篇 |
1996年 | 356篇 |
1995年 | 283篇 |
1994年 | 236篇 |
1993年 | 170篇 |
1992年 | 146篇 |
1991年 | 125篇 |
1990年 | 88篇 |
1989年 | 74篇 |
1988年 | 62篇 |
1987年 | 42篇 |
1986年 | 52篇 |
1985年 | 17篇 |
1984年 | 36篇 |
1983年 | 26篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 15篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 21篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
激光光束质量诊断技术的进展 总被引:1,自引:0,他引:1
本文介绍了激光光束质量诊断技术近年来的进展,以及国际标准化组织推荐的聚集光束测量法,指出了该技术的发展方向。 相似文献
102.
阐述了新型线圈式磁弹性扭矩传感器的原理,推导出其输出表达式,进而说明了线圈式磁弹性扭矩传感器具有输出平稳、响应快的特点。 相似文献
103.
Fatigue behavior and morphology of long glass fiber reinforced semicrystalline polyamide (nylon 6,6) and amorphous polycarbonate (PC) composites were investigated. The fiber length distribution in the molded samples was calculated by image analyzer. The tension-tension fatigue loading tests at various levels of stress amplitudes were studied. The two-parameter Weibull distribution function were applied to obtain the statistical probability distribution of experimental data. A good correlation existed between the experimental data and the Weibull distribution curves. Straight line S? N curves of long glass fiber reinforced semicrystalline polyamide and amorphous polycarbonate composites at various probabilities were established. The stiffness of the composite under tension-tension fatigue loading was measured. The thermal stress history was also investigated by thermo-imaging techniques during fatigue life testing. Further, failure morphology was examined by scanning electron microscopy (SEM). The results showed that the fracture behavior of the ductile damage in polyamide is different from the brittle damage in polycarbonate. 相似文献
104.
105.
The feasibility of the anodic protection of titanium evaporators in Al2(SO4)3 solution was studied by the measurement of polarization curves, weight loss, solubility of passive film and AC impedance. The protection parameters and efficiency were determined. In addition, the practical technology of anodic protection was studied by screening reference electrodes and auxiliary cathodes. Throwing power was also measured. Four rows of tube-type evaporators of titanium have been anodically protected in situ. Field tests lasting more than one year show satisfactory results. 相似文献
106.
An extensive Markov process, which considers both the coding redundancy and the intersample redundancy, is presented to measure the entropy value of an ECG signal more accurately. It utilizes the intersample correlations by predicting the incoming n samples based on the previous m samples which constitute an extensive Markov process state. Theories of the extensive Markov process and conventional n repeated applications of m-th order Markov process are studied first. After that, they are realized for ECG exact coding. Results show that a better performance can be achieved by the authors' system. The average code length for the extensive Markov system on the second difference signals was 2.512 b/sample, while the average Huffman code length for the second difference signals was 3.326 b/sample 相似文献
107.
108.
In Kwon Kim Rae-Hong Park 《IEEE transactions on image processing》1996,5(4):587-597
In this paper, we propose a coding algorithm for still images using vector quantization (VQ) and fractal approximation, in which low-frequency components of an input image are approximated by VQ, and its residual is coded by fractal mapping. The conventional fractal coding algorithms indirectly used the gray patterns of an original image with contraction mapping, whereas the proposed fractal coding method employs an approximated and then decimated image as a domain pool and uses its gray patterns. Thus, the proposed algorithm utilizes fractal approximation without the constraint of contraction mapping. For approximation of an original image, we employ the discrete cosine transform (DCT) rather than conventional polynomial-based transforms. In addition, for variable blocksize segmentation, we use the fractal dimension of a block that represents the roughness of the gray surface of a region. Computer simulations with several test images show that the proposed method shows better performance than the conventional fractal coding methods for encoding still pictures. 相似文献
109.
In recent years, three‐dimensionally (3D) braided composites have attracted a great deal of attention because of their high‐impact damage tolerance and fatigue life, superior fracture toughness, and so forth, and have been used in aeronautics, military, and transportation. These advantages make them strong candidates for osteosynthesis devices. In this study, 3D braided carbon fiber–epoxy (C3D/EP) composites were produced via a simple vacuum impregnation technique. The load‐deflection curve, mechanical properties, and influence of fiber volume fraction, braiding angle, and axial reinforcing fibers were examined to determine their suitability for internal fixation devices. It is found that the C3D/EP composites have excellent toughness and do not show brittleness when fractured because of their relatively high void content. The flexural, shear, and impact strengths of the C3D/EP composites are excellent. It was shown that a C3D/EP composite with a stiffness similar to load‐bearing bones can be made while maintaining enough strength. It is concluded that a relatively higher void content and braiding angle is more suitable for the C3D/EP composites from the viewpoint of requirements of fracture fixation materials. The moisture absorption behavior and changes in mechanical properties caused by moisture uptake were evaluated. Results show that absorbed moisture slightly decreases mechanical properties of the C3D/EP composites. Contrary to the unreinforced epoxy, the moisture absorption behavior of the C3D/EP composites cannot be described with Fick's law of diffusion, probably because of the presence of voids and/or 3D fiber structure. The exact mechanisms should be proposed in further investigations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1031–1039, 2002 相似文献
110.
Youngwoo Kwon Sovero E.A. Deakin D.S. Higgins J.A. 《Microwave Theory and Techniques》1998,46(9):1237-1241
A 44-GHz monolithic waveguide plane-wave amplifier (PWA) with improved unit cell design is presented in this paper. The unit cell is a two-stage direct-coupled design and satisfies size, bistability, and stability requirements of the waveguide PWA. The ultra-compact unit cell had a cell size of 0.8 mm2, and showed a small-signal gain of 8 dB and an output power of 15 dBm at 44 GHz with a corresponding dc-to-RF efficiency of 10%. A monolithic waveguide PWA using these unit cells showed a “flange-to-flange” gain of 5 dB, an output power of 0.3 W, and an efficiency of 2% at 44 GHz 相似文献